Printed images produced by a printing press have been checked, for a considerable length of time, for their respective quality by the operators of printing presses. A classification of the printed images into good or poor quality is performed in the course of this quality checking. The printed image of these printed products is classified as being either good or poor, with a poor image typically containing errors.
A method for detecting and for controlling the quality of printed products, in particular during the printing process, is known from DE 40 23 320 A1. An evaluation of each sheet takes place in a primary phase, which assigns the classification “good” or “poor” to each sheet. After the detection of a sheet containing an error, in a secondary phase three actual color images of the printed product are additionally employed, with the aid of an expert system, for the determination of the type of error. An alarm signal is triggered if a preset number of sheets, with such errors, is exceeded.
A method for comparing the printed image of detected images with a reference image is disclosed in DE 199 40 879 A1. The images to be compared are digitized in the form of pixel data and are stored.